Hundreds of recovered bicycles sit in the warehouse in Hunters Point. More than 4,000 bikes were stolen in San Francisco last year, and only 142 were returned to owners by police.

Photo: Brant Ward, The Chronicle

Hundreds of recovered bicycles sit in the warehouse in Hunters...

Image 6 of 10

Many of the bicycles have evidence tags on them Tuesday November 26, 2013 in San Francisco, Calif. At a San Francisco Police department evidence site, about 800 stolen and recovered bicycles are stored. Some will be rebuilt and fixed up for children in the city.

Photo: Brant Ward, The Chronicle

Many of the bicycles have evidence tags on them Tuesday November...

Image 7 of 10

Lieutenant Joe Cordes walks past the stable of bicycles near the entrance to the storage facility Tuesday November 26, 2013 in San Francisco, Calif. At a San Francisco Police department evidence site, about 800 stolen and recovered bicycles are stored. Some will be rebuilt and fixed up for children in the city.

Photo: Brant Ward, The Chronicle

Lieutenant Joe Cordes walks past the stable of bicycles near the...

Image 8 of 10

Some of the road bikes look like they were expensive Tuesday November 26, 2013 in San Francisco, Calif. At a San Francisco Police department evidence site, about 800 stolen and recovered bicycles are stored. Some will be rebuilt and fixed up for children in the city.

Photo: Brant Ward, The Chronicle

Some of the road bikes look like they were expensive Tuesday...

Image 9 of 10

Bicycles are stored in police barricades, which double as bike racks in the storage area Tuesday November 26, 2013 in San Francisco, Calif. At a San Francisco Police department evidence site, about 800 stolen and recovered bicycles are stored. Some will be rebuilt and fixed up for children in the city.

Photo: Brant Ward, The Chronicle

Bicycles are stored in police barricades, which double as bike...

Image 10 of 10

Lieutenant Joe Cordes looks over a tag on a bike at the storage facility Tuesday November 26, 2013 in San Francisco, Calif. At a San Francisco Police department evidence site, about 800 stolen and recovered bicycles are stored. Some will be rebuilt and fixed up for children in the city.

Collecting dust in an evidence warehouse in Hunters Point are several hundred bicycles stolen on the streets of San Francisco.

There are rows of mountain bikes, road bikes, rusted clunkers, fat-tired cruisers, fancy carbon fiber, and new and old frames of every color.

The cycling cache, which recently stood at more than 800, is the fruit of the San Francisco Police Department's labor - the bicycles were recovered in stings, raids, stakeouts and chop shop busts - yet none of the bicycles has been claimed.

The problem, according to Officer Matt Friedman, the department's point man on bicycle theft, is that there's no way to find the rightful owners.

"We haven't been able to identify the owners," Friedman said. "It's just an ongoing issue that the SFPD is continually responding to. ... We need more people to actually report bike theft, to know their serial numbers and to take pictures of their bikes."

The crowded warehouse is a stark reminder of just how many bicycle thieves are freewheeling around San Francisco and how difficult it is to stop them.

Cycling at forefront

The problem is an outgrowth of a cycling renaissance in San Francisco that has, in turn, exposed a snowball effect of flaws in the system. For instance, few bicycles are registered, there is no citywide system to keep track of them, and there is no organized way for victims to find their property. Without that information, most bike thefts go unreported, crimes cannot be pinned on culprits, and recovered bicycles are rarely claimed.

An estimated 4,085 bicycles were stolen in San Francisco last year, according to the 2012 State of Cycling Report released recently by the city's budget and legislative analyst. But police received only 817 reports of bike thefts or attempted thefts because such crimes are significantly underreported, Friedman said.

Nearly half of the reported thefts occurred in downtown areas, including Union Square, the Tenderloin, Civic Center, Market Street, South of Market and along the Embarcadero.

"The numbers are pretty astounding," said Kit Hodge, the deputy director of the 12,000-member San Francisco Bicycle Coalition. "It's definitely a growing problem. We're very interested in working with the city to reduce the amount of theft."

Getting back bikes

Police recovered 864 stolen bicycles last year, but only 142 were returned to their owners. The report said few bicycle owners record the serial numbers on their frames, take photographs or record other identifying details. Even if they did, it stated, no coordinated bicycle registry program exists that officers could refer to when they recover a bike.

Also, the study found, bicycle theft investigations are generally not given high priority. That's because there are not enough officers or resources available and other more serious crimes generally take precedence. The San Francisco District Attorney's Office does not have data on the number of people prosecuted for bicycle theft. Police and bicycle advocates believe only a small fraction of thieves are ultimately brought to justice.

"You see a suspicious guy with a bike, you run the serial number and it comes back negative, so what you have is a guy with an expensive bike," Friedman said. "What do you arrest him for? It's the same with the chop shops. If I'm going to take somebody's liberties away, I've got to have proof."

Police know, for instance, that there is a bicycle theft ring that operates in and around Civic Center and that there are chop shops throughout the city where bicycles are taken apart and rebuilt or valuable parts are removed, but until now they have not been able to do a lot about it.

Policing by Twitter

The wheels of justice are finally beginning to turn, according to city politicians and police, who are joining forces in an attempt to halt what everyone agrees is an ever more sophisticated crime network.

Friedman recently established a Twitter account -@sfpdbiketheft - where residents can report thefts or post photographs of lost bicycles or mug shots of bicycle theft suspects. The Twitter account was recently used to connect theft suspects spotted in Golden Gate Park loading bicycles into a van to a burglary in the Richmond District. A carbon fiber Colnago and a rare Eddy Merckx racing bike, worth about $8,000, were returned to the owner, Friedman said.

The bicycle coalition and police are setting up workshops on bike-locking techniques, garage security and other antitheft strategies. Officers at the Mission Station have held two workshops, one of which was co-sponsored by Google. The nonprofit group San Francisco Safe, or Safety Awareness for Everyone, is in the process of setting up a citywide online bicycle registry program.

City officials and businesses are working together to build more secure bicycle parking structures, but bike theft is difficult to stay on top of, Friedman said. Pilfered bicycles are showing up in increasing numbers on Craigslist, he said, and he has recovered nearly a dozen over the past few months that were stolen and listed for sale on the site.

"It's a regional problem," he said, adding that he has been trying without luck to reach someone at Craigslist to figure out how to prevent the sale of stolen bicycles. "We really need to take a regional approach to this problem and work with bicycle coalitions and police agencies and really start a regional task force."

Craigslist representatives could not be reached for comment.

2-wheel commuters

The growth in thievery has come at a time when the number of San Franciscans commuting by bicycle is at an all-time high. Bicycle commuting has grown 71 percent since 2007, according to the city's cycling report. San Francisco is now third in the nation in ridership behind Portland, Ore., and Seattle.

Market Street alone saw a 43 percent increase in the number of people cycling between 2010 and 2011, the largest jump in the number of pedalers in any single year. Infrastructure improvements, including a new bicycle-sharing program, have had a lot to do with it. The San Francisco Municipal Transportation Agency has put in new bikeways and bicycle lanes on Market Street, John F. Kennedy Drive, Cargo Way and Cesar Chavez Street. More than 25 miles of bike lanes have been added over the past six years, bringing the citywide total to 65 miles.

Two hundred of the 858 bicycles in the evidence warehouse were recently donated to charity, police said. The Bicycle Coalition and the city's Human Services Agency agreed to refurbish them, but that still leaves more than 600 unclaimed bicycles and, undoubtedly, plenty more to come. Hopefully, Friedman said, there will eventually be enough information circling around the city for the owners to be reunited with their property.

Find your bike

Looking for a bicycle stolen in San Francisco? Here are things you can do:

Online: Go to www.parkstation.org and click on the "Anti Bike Theft Unit" link on the left-hand side.